Before the advent of synthetic fibers, down was widely used as the insulator for sleeping bags and protective clothing. Down is a small feather cluster and is sectioned off in small areas (quilted) to keep it from shifting within the bag or clothing. The internal cavity of a down sleeping bag is designed to fill in around the body and confine the body heat to the body. Down has excellent lofting characteristics which contribute to the action of the down settling closely around the body allowing few air pockets and little area to be heated by the body. It is the primary reason down has been used as an insulator, but the quilting of the down to keep it from shifting within the bag or clothing inherently inhibits lofting and results in cold spots coinciding with the quilting stitches.
The amount of loft in the insulators of sleeping bags and protective clothing is a measure of the warmth provided their occupants. Generally, the more loft, the warmer the occupant.
Synthetic fibers have been found to have the capacity for lofting when used as insulators. There are currently two types of synthetic fibers used as insulators for sleeping bags, namely, chopped staple fibers and bonded continuous filament fibers. Both are advantageous over down in that the synthetic fibers will not absorb water and will permit evaporation of body moisture through the fibers. Synthetic fibers are supplied in rolls, like yard goods, to the manufacturers of insulators for sleeping bags and protective clothing. The rolls of fibers are then cut into layers of desired dimensions and weight.
Chopped staple fibers are used as an insulator between the outer shell and the inner liner of the quilted sleeping bag shown in Lauren D. Worley U.S. Pat. No. 3,584,323 issued Sept. 10, 1969 for MULTI-PURPOSE SLEEPING BAG CONSTRUCTION. The quilting lessens the loft of the chopped staple and defines cold spots coinciding with the quilting stitches.
Bonded continuous filament fibers used in quilted insulators are subject to the same objection--inhibition of loft and cold spots coinciding with the quilting stitches.
Bonded continuous filament fibers have also been used in unquilted insulators secured only by perimeter stitching to the shell and liner fabrics. The unquilted insulators formed from bonded continuous filament fibers are advantageous over quilted insulators formed from the same material because the lofting of fibers is unrestricted by quilt stitches and a uniform loft is achieved throughout the area of the insulator. The prior art insulator of unquilted but bonded continuous filament fiber is approximately the same weight as a down insulator made for the same temperature range.
Each layer of bonded continuous filament fibers has a resin finish bonded and heat set on each surface of the layer which holds the surface fibers together and enables satisfactory handling of the fibers during manufacture of an insulator. However, the bonding of the fibers with resin restricts the amount of loft.
The prior art insulator of unquilted but bonded continuous filament fiber retains its original loft after being washed and, in fact, has a slight increase in loft after each of its first five or six washes. The increase in loft of bonded continuous filament insulators after washing is in sharp contrast to the loss of loft following washing of quilted sleeping bags made from down or chopped staple.
It has been found that the amount of loft in an insulator made from continuous filament fibers can be increased significantly by eliminating the resin bonding previously thought necessary to control the fibers while making insulators. Insulators made from unquilted and unbonded continuous filament fibers have 2 to 3 times the loft of the prior art insulators made from unquilted but bonded continuous filament fibers.